Cells in the kidney and heart respond to hypertensive and other stresses by undergoing hypertrophic growth. While compensatory hypertrophy is not generally associated with disease, the excessive hypertrophy incurred by chronic stresses can lead ultimately to organ failure. Such pathologic hypertrophy is a major factor in the progression of a number of clinically important conditions including dilated cardiomyopathy and diabetic renal failure. Accordingly, the development of novel treatment modalities to combat pathologic hypertrophy would be of tremendous benefit. It is becoming apparent that cellular signal transduction mechanisms activated by stress mediate the progression to hypertrophy. However, the mechanisms by which these signaling pathways elicit hypertrophy are poorly understood. We have identified an immediate early gene product, Gene 33, that is transcriptionally induced by pro-hypertrophic stress stimuli including unilateral nephrectomy and end stage diabetic renal failure. The molecular structure of Gene 33 indicates a docking or scaffolding protein implicated in the nucleation of signal transduction complexes and, possibly, in the regulation of the actin cytoskeleton. Consistent with this is the observation that transient expression of Gene 33 elicits activation of the stress-activated protein kinase (SAPK also called JNK) signal transduction pathway, and reorganization of the actin cytoskeleton--two responses required for the hypertrophic phenotype. Gene 33 can also bind Ras superfamily GTPases in vivo and, in a GTP-dependent manner, in vitro. Thus, Gene 33 may be a stress-induced protein that itself coordinates and maintains an overall cellular response to pro-hypertrophic stress. Consequently, the continued presence of Gene 33 may ultimately give rise to hypertrophy. To test this hypothesis we propose three Aims: (1) we will determine which stress signaling pathways are required for Gene 33 induction. We propose that mitogen-activated protein kinase (MAPK)/extracellular signal- regulated kinase (ERK) pathways and/or the calcineurin-nuclear factor of activated T cells (NFAT) pathway mediate Gene 33 induction. Dominant inhibitory and constitutively active constructs as well as pharmacologic agents will be used to manipulate these pathways and standard molecular biological techniques will be used to track Gene 33 expression in response to pathway manipulation. (2) We will determine the mechanisms by which Gene 33 elicits activation of SAPK. Gene 33 has no apparent enzymatic properties, and we believe that it binds proteins upstream of SAPK, thereby promoting SAPK pathway activation. We will use both genetic and biochemical methods to identify molecular species that couple Gene 33 to the SAPKs. (3) We will use immunocytochemical and biochemical methods to determine if Gene 33 can elicit the cytoskeletal changes associated with hypertrophy, and if expression of Gene 33 can induce a hypertrophic phenotype. These studies will identify the molecular mechanisms by which Gene 33 alters cell function and will provide novel targets for anti hypertrophic therapeutics.